(a) Technical Field
The present invention relates to a highly heat resistant sound absorbing material for a vehicle. More particularly, the present invention relates to a highly heat resistant sound absorbing material for a vehicle including a fiber material having a limiting oxygen index (LOI) of at least 25% and which maintains its shape at a temperature of about 200° C. or above, and a thermosetting binder resin which maintains its shape at a temperature of about 200° C. or above The fiber material and thermosetting binder resin are provided at a specific proportion to form a sound absorbing material that maintains its shape even at high temperatures of about 200° C. or above and that satisfies UL 94V-0 flame retardancy.
(b) Background Art
Various kinds of noise are generated during operation of a vehicle. The vehicle noise mainly emanates from an engine or an exhaust system and is transmitted into the passenger compartment of the vehicle via air. A sound absorbing material has been used to reduce the noise emanating from the engine and the exhaust system and transmitted into the passenger compartment. An insulation dash, a dash isolation pad, etc., are used to prevent noise from the engine from being transmitted into the passenger compartment. Further, a tunnel pad, a floor carpet, etc., are used to prevent noise from the exhaust system from being transmitted into the passenger compartment.
As a sound absorbing material for a vehicle, Korean Patent Application Publication No. 2004-0013840 describes insertion of a synthetic resin film layer that is 40-100 μm thick in a length direction into a 20-mm thick PET fiber layer. Korean Patent Application Publication No. 2002-0089277 describes preparation of a sound absorbing insulation in the form of a nonwoven fabric by cutting and beating out a polyester fiber and an acrylic fiber, mixing with a low-melting-point polyester fiber, and heating. Korean Patent Application Publication No. 2006-0043576 describes a method of coating at least one of an upper layer and a lower layer of a polyester (PET) felt using a fiber mixture of a low-melting-point fiber (LMF) and a regular fiber.
However, the presently known sound absorbing materials for vehicles are limited in that their weight needs to be increased in order to reduce noise from the engine and the exhaust system. Further, the resulting noise reduction is unsatisfactory considering the increased weight. To overcome this limitation, it is necessary to apply the sound absorbing material as close to the source of noise from the engine and the exhaust system as possible. However, for such application of the sound absorbing material close to the source of noise from the engine and the exhaust system, the sound absorbing material must be capable of maintaining its shape even at high temperatures of about 200° C. or above, and must further possess superior flame retardancy.